VEGF upregulates TF activity and mRNA in HUVEC. (A) VEGF induces TF activity in a dose-dependent manner. TF activity equivalents were determined in a one-stage clotting assay. Incubation of cells with increasing concentrations of VEGF in the range of 0.125 to 5 nmol/L for 4 hours. (B) Incubation with 1.25 nmol/L VEGF for 0.5 , 1, 2, 4, and 6 hours. For comparison, kinetics of TF induction by TNF- (100 U/mL) is shown. Each value is the mean ± SD of triplicate in one experiment representative of five performed with similar results. (C) VEGF upregulates TF mRNA in HUVEC: Northern blot analysis of total RNA (20 μg) extracted from unstimulated cells and cells treated with VEGF for 2 and 4 hours. This experiment is representative of two experiments done with similar results.